Coding & Algorithms Interview Questions
Practice 2,960 real Coding & Algorithms interview questions for 2026. Coding & Algorithms interview questions for top tech firms like Meta, Amazon, Google, Uber, and TikTok — real questions from actual interviews with detailed solutions — to power your interview preparation. This collection is sharply focused on algorithmic patterns (arrays, strings, sliding windows, trees/graphs, dynamic programming, greedy, two-pointers, and hashing), clean, review-ready code, and the explanation skills that distinguish hires. In 2026 expect familiar medium-to-hard problems plus newer twists: AI-enabled or multi-file coding rounds at some companies, more emphasis on explainability and edge-case reasoning, and occasional real-world performance constraints (streaming, concurrency, memory limits). Interviewers evaluate problem framing, algorithm choice, complexity trade-offs, test-case thinking, and communication under time pressure. Best prep mixes pattern-based practice, timed mock interviews, code-review style polishing, and rehearsed explanations of complexity and tradeoffs. Focus your last-mile prep on writing correct, readable code quickly and on explaining why your solution is robust and efficient for production scenarios.
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Optimize Trapping Rain Water
Question LeetCode 42. Trapping Rain Water – implement a brute-force solution, analyze its complexity, then optimize to an O(n) solution with O(n) spac...
Count closed islands in a grid
Problem You are given an m x n 2D grid representing a map after flooding: - 0 = water - 1 = land An island is a maximal 4-directionally connected comp...
Find Missing Ranges with Bounds
Given a sorted array of distinct integers nums and two integers lower and upper that define an inclusive interval [lower, upper], return all maximal r...
Extract stream prefix before stop token
You are consuming a text stream delivered as an iterator/generator of string chunks (each chunk may be any length, including empty). You are also give...
Compute expected days until no whole pills
A bottle initially contains H half-pills and W whole pills. Each day: 1. You randomly select one pill uniformly from the bottle. 2. If it is a half-pi...
Implement a Maximum-Tracking Stack
Design a stack-like data structure that supports the following operations efficiently: - push(x): Push integer x onto the stack. - pop(): Remove and r...
Print directory tree with indentation
You are given a root directory of a filesystem represented as a tree. Each node is either a directory (can have children) or a file (no children). Pri...
Implement Linear Regression Training
Implement a function train_linear_regression(X, y, lr, epochs) that trains a linear regression model from scratch using batch gradient descent. Requir...
Find flush and straight groups in cards
You are given an array of strings cards, where each string represents a distinct playing card. Each card string has the format <rank><suit>: - rank is...
Implement phrase search and JSON path
The coding rounds included two concrete implementation tasks: 1. In-memory document phrase search - You are given a list of documents, each represe...
Solve Watcher Simulation And Integer Conversion
You are asked to solve two independent coding tasks. Task 1: Count players that reach the finish There is a one-dimensional track with integer positio...
Compute Range Sum Quickly
Given an integer array nums and two indices left and right (inclusive), return the sum of the elements from nums[left] to nums[right]. You should disc...
Implement tag matcher and filesystem
This interview reportedly included two coding problems: 1. Tag matching in text Given a sentence and a list of tags or keywords, return the tags th...
Detect duplicate files by content
Detect duplicate files by content in a filesystem. Given access to a directory tree, return groups of file paths that have identical byte content. Min...
Decide and implement DP/heap and approximation
You have 90 minutes to complete three related coding tasks: a) Dynamic programming: Given an integer array nums (n ≤ 2e 5) and a threshold T, design a...
Compute max coins with 3-step token moves
You are given a one-dimensional board with n positions represented by a string s of length n: - . = empty cell - T = token - C = coin You may move tok...
Solve two array and string problems
You will solve two independent coding tasks. Problem 1: Generate All Subsets of a Set You are given an integer array nums containing n distinct elemen...
Find max word letter span
Implement a function that, given an input text string, computes the maximum word letter span and returns both (a) the maximum span and (b) the list of...
Implement multi-part cost calculator
You are given a price catalog and a list of orders. Implement the following in any language (Python examples acceptable): Inputs - price_catalog: mapp...
Reconstruct itinerary with lexicographic ties
You are given m airline tickets as directed pairs [from, to]. Build an itinerary that starts at a specified airport start (e.g., "JFK") and uses every...